In recent years, composite materials comprising highly filled polymers have become commonly used for dental restorations. Current composite materials contain crosslinking acrylates or methacrylates, inorganic fillers such as glass or quartz, and a photoinitiator system suitable for curing by visible light. Typical methacrylate materials include 2,2′-bis[4-(2-hydroxy-3-methacryloyloxypropyl)phenyl]propane (“Bis-GMA”); ethoxylated Bisphenol A dimethacrylate (“EBPDMA”); 1,6-bis-[2-methacryloyloxyethoxycarbonylamino]-2,4,4-trimethylhexane (“UDMA”); dodecanediol dimethacrylate (“D3MA”); and triethyleneglycol dimethacrylate (“TEGDMA”). The structural formulae for these are shown below.

Dental composite materials offer a distinct cosmetic advantage over traditional metal amalgam. However, they do not offer the longevity of amalgam in dental fillings. The primary reason for failure is excessive shrinkage during photopolymerization in the tooth cavity, which can cause leakage and bacterial reentry. Another reason is they have inadequate strength and toughness, as reflected in the measured properties of flexural strength and fracture toughness. Hence, there is still a need for new monomers and new monomer combinations which, when polymerized, impart high fracture toughness and flexural strength in the resulting composite. It is also highly desirable to have low shrinkage stress on polymerization.
One of the more common commercially used monomers is Bis-GMA. However, it is highly viscous at room temperature and difficult to work with. It is therefore diluted with a second, lower viscosity polymerizable component (“fluidizer”), a methacrylate monomer, such as TEGDMA, tetraethylene glycol dimethacrylate, or docecanediol dimethacrylate. However, while providing low viscosity, lower viscosity components (generally low molecular weight monomers) can contribute to increased shrinkage. Increasingly, Bis-GMA and TEGDMA have been combined with UDMA and EBPDMA, but shrinkage remains high enough that improvement is desirable.
A more efficient and effective fluidizing monomer that would allow dental composites to be formulated with higher proportions of the high-viscosity monomer while not compromising the mechanical properties or polymerization shrinkage of the system is a desirable invention. An effective fluidizing monomer could also allow the composite to be formulated at a higher filler level, further lowering shrinkage.
(Meth)acrylated adducts of caprolactone and tricyclodecanemethylol have been described as resinous coating materials for optical fibers in U.S. Pat. No. 4,843,111, but not for dental composite applications.
An adduct prepared by reaction of cyclohexanedimethanol mono(meth)acrylates with lactones has been described in JP 2000016967 for coating systems, but not for dental composite applications.
Adducts prepared by reaction of cyclohexanedimethanol with caprolactone and subsequently (meth)acrylated have been described in JP2000169431 for inks, but not for dental composite applications.
Adducts of 1,4-cyclohexanedimethanol and caprolactone, not (meth)acrylated, have been described in U.S. Pat. No. 5,159,047 for coating systems, but not for dental composite applications.
A copolymer of adipic acid (erroneously translated from the Japanese as “acrylic acid” in Chemical Abstracts 136:233450), ε-caprolactone, and 2-methyl-1,1-cyclohexanedimethanol has been described in JP 2002069163 as a precursor to spandex filaments, but not for dental composite applications.
There thus remains a need for efficient and effective fluidizing monomers for dental composite materials that combine reduced shrinkage with sufficiently low viscosity, high polymerization rate, and acceptable mechanical properties.